Bragg-like gratings on high refractive index material

ABSTRACT

Techniques for fabricating a slanted structure are disclosed. In one embodiment, a method for fabricating a slanted structure on a material layer includes forming a mask layer on the material layer, and implanting ions into a plurality of regions of the material layer at a slant angle greater than zero using an ion beam and the mask layer. The slant angle is measured with respect to a surface normal of the material layer. Implanting the ions into the plurality of regions of the material layer changes a refractive index or an etch rate of the plurality of regions of the material layer. In some embodiments, the method further includes wet-etching the material layer using an etchant to remove materials in the plurality of regions of the material layer. In some embodiments, the method includes either simultaneous or post-implantation etching of modified material through a dry etching process using reactive etchants in feed gas.

BACKGROUND

An artificial reality system, such as a head-mounted display (HMD) orheads-up display (HUD) system, generally includes a display configuredto present artificial images that depict objects in a virtualenvironment. The display may display virtual objects or combine imagesof real objects with virtual objects, as in virtual reality (VR),augmented reality (AR), or mixed reality (MR) applications. For example,in an AR system, a user may view both images of virtual objects (e.g.,computer-generated images (CGIs)) and the surrounding environment by,for example, seeing through transparent display glasses or lenses (oftenreferred to as optical see-through) or viewing displayed images of thesurrounding environment captured by a camera (often referred to as videosee-through).

One example optical see-through AR system may use a waveguide-basedoptical display, where light of projected images may be coupled into awaveguide (e.g., a substrate), propagate within the waveguide, and becoupled out of the waveguide at different locations. In someimplementations, the light of the projected images may be coupled intoor out of the waveguide using a diffractive optical element, such as aslanted grating (e.g., a surface-relief or Bragg-like grating). In manycases, it may be challenging to fabricate the slanted grating with thedesired profile at a desirable yield and productivity.

SUMMARY

This disclosure relates generally to techniques for fabricating slantedstructures, and more specifically, to techniques for making slantedstructures (e.g., slanted gratings) on various materials, such assilicon nitride, organic materials, or inorganic metal oxides, etc. Forsome materials, a slanted ion implementation technique may be used tomodify the refractive index of a material layer (e.g., a substrate) toform a slanted grating, or to modify the etch rate of the material layersuch that the material layer may be selectively etched to remove theion-implanted regions to form a slanted structure. For some materials, aconcurrent or sequential ion bombardment-based material modificationtechnique may be used in conjunction with a reactive gas tosimultaneously modify and remove the material, thereby forming slantedgratings as defined by a hard mask. The slanted structures obtained bythe processes and techniques disclosed herein can have a large slantangle, a high depth, and similar slant angles for the leading edge andtrailing edge of a ridge.

In some embodiments, the slant angle of the slanted structure (e.g., aslanted grating) can be changed by changing the incident angle of ionswith respect to the substrate during the ion implantation. The energy ofthe ions can be modified to change a depth of the slanted grating.Further, the composition of the ions can be modified through appropriateselection of feed gas mixture, ion source, and extraction parameters.The refractive index of the implanted region can be modified bymodifying the concentration of the implanted ions. In some embodiments,the slant angle, ion energy, and/or ion concentration can be varied overdifferent regions of the slanted grating. In some embodiments, similartechniques may be applied to an overcoat layer for the slanted grating.

In some embodiments, a method of fabricating a slanted structure on amaterial layer may include forming a mask layer on the material layer,and implanting ions into a plurality of regions of the material layer ata slant angle greater than zero using an ion beam and the mask layer,where the slant angle is measured with respect to a surface normal ofthe material layer. Implanting the ions into the plurality of regions ofthe material layer may change a refractive index or an etch rate of theplurality of regions of the material layer. In some embodiments, thematerial layer may include one or more of a transparent substrate, asemiconductor substrate, a SiO2 layer, a Si3N4 material layer, atitanium oxide layer, an alumina layer, a SiC layer, a SiOxNy layer, anamorphous silicon layer, a spin on carbon (SOC) layer, an amorphouscarbon layer (ACL), a diamond like carbon (DLC) layer, a TiOx layer, anAlOx layer, a TaOx layer, and an HFOx layer. In some embodiments, theions may include hydrogen ions or oxygen ions.

In some embodiments, the method of fabricating the slanted structure mayinclude wet-etching the material layer using an etchant to removematerials in the plurality of regions of the material layer. In someembodiments, the material layer may include a Si₃N₄ material layer, theions may include hydrogen ions, and the etchant may include a dilutedhydrofluoric acid. In some embodiments, the method may further includeperforming the implanting and wet-etching repeatedly until apredetermined depth of the slanted structure is reached. In someembodiments, the predetermined depth of the slanted structure is greaterthan 100 nm.

In some embodiments, implanting ions into the plurality of regions ofthe material layer at a slant angle greater than zero may include atleast one of rotating the material layer during the implanting to varythe slant angle for the plurality of regions, or changing an ion energyof the ions during the implanting to change an implantation depth forthe plurality of regions. In some embodiments, the method may furtherinclude wet-etching the material layer using an etchant to removematerials in the plurality of regions of the material layer, removingthe mask layer, and forming an overcoat layer on the material layer. Insome embodiments, the method may further include performing ionimplantation on the overcoat layer to change refractive indexes in someregions of the overcoat layer. The overcoat layer may include, forexample, one or more of fluorinated SiO₂, porous silicate, SiO_(x)N_(y),HFO₂, and Al₂O₃.

In some embodiments, implanting ions into the plurality of regions ofthe material layer may include implanting different amounts of ions intodifferent regions of the plurality of regions by using different ioncurrents for the ion beam, different implantation times, or both whenimplanting different regions of the plurality of regions. In someembodiments, the material layer may include a Si₃N₄ material layer, andthe ions may include oxygen ions. In some embodiments, the slant anglemay be greater than 45°.

In some embodiments, an ion implantation system for fabricating aslanted optical device on a substrate may include an ion source forgenerating ions of a chemical element, an accelerator forelectrostatically accelerating the ions, and a target chamber includinga supporting structure, where the supporting structure may be configuredto hold the substrate and is rotatable with respect to a movingdirection of the ions. In some embodiments, ion implantation system mayalso include a controller configured to change a rotation angle of thesupporting structure such that the ions impinge on the substrate at apredetermined slant angle.

In some embodiments of the ion implantation system, the controller maybe configured to control at least one of a speed of the ions, a flux ofthe ions, an implantation time, a rotation speed of the supportingstructure, or a linear moving speed of the supporting structure. In someembodiments, the controller may further be configured to rotate thesupporting structure to different rotation angles for implantingdifferent regions of the substrate, accelerate the ions to differentspeeds for implanting different regions of the substrate, or implantingdifferent numbers of ions into different regions of the substrate. Insome embodiments, the chemical element may include hydrogen or oxygen,and the substrate may include a Si₃N₄ layer.

In some embodiments, a slanted surface-relief grating may be obtained bya process, where the process may include forming a mask layer on amaterial layer, implanting ions into a plurality of regions of thematerial layer at a slant angle greater than 30° (measured with respectto a surface normal of the material layer) using an ion beam and themask layer, and wet-etching the material layer using an etchant toremove materials in the plurality of regions of the material layer. Insome embodiments, the material layer may include a Si₃N₄ material layer,the ions may include hydrogen ions, and the etchant may include adiluted hydrofluoric acid. In some embodiments, the process may furtherinclude performing the implanting and wet-etching repeatedly until apredetermined depth of the slanted surface-relief grating is reached,where the predetermined depth may be greater than 100 nm.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified diagram of an example near-eye display accordingto certain embodiments.

FIG. 2 is a cross-sectional view of an example near-eye displayaccording to certain embodiments.

FIG. 3 is an isometric view of an example waveguide display according tocertain embodiments.

FIG. 4 is a cross-sectional view of an example waveguide displayaccording to certain embodiments.

FIG. 5 is a simplified block diagram of an example artificial realitysystem including a waveguide display.

FIG. 6 illustrates an example optical see-through augmented realitysystem using a waveguide display according to certain embodiments;

FIG. 7 illustrates propagations of display light and external light inan example waveguide display.

FIG. 8 illustrates an example slanted grating coupler in an examplewaveguide display according to certain embodiments.

FIGS. 9A-9C illustrate an example process for fabricating a slantedsurface-relief structure according to certain embodiments.

FIG. 10 illustrates an example slanted surface-relief structureaccording to certain embodiments.

FIG. 11A illustrates an example substrate on which a slanted structuremay be formed using a mask according to certain embodiments.

FIG. 11B illustrates an example slanted ion implantation processaccording to certain embodiments.

FIG. 11C illustrates an example slanted surface-relief structure formedon a substrate after ion implantation and etch processes according tocertain embodiments.

FIG. 12 illustrates an example process for fabricating slantedstructures with different refractive indexes on a substrate according tocertain embodiments.

FIG. 13 illustrates an example process for fabricating slantedstructures with different depths on a substrate according to certainembodiments.

FIG. 14 illustrates an example process for fabricating slantedstructures with different slant angles on a substrate according tocertain embodiments.

FIG. 15 is a simplified flow chart illustrating an example method offabricating a slanted surface-relief structure according to certainembodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Techniques disclosed herein relate generally to micro- or nano-structuremanufacturing. More specifically, and without limitation, thisapplication relates to techniques for fabricating micro or nano slantedstructures. In some embodiments, it is found that it is desirable tofabricate slanted structures for manipulating behaviors of light. Someof the benefits of the slanted structures may include a high efficiencyof light transfer, a large variation in refractive indices, and/or thelike. It is also found that the parallel slanted (with respect to theplane of the surface being etched) structures with constant or variableslant parameters solve a problem unique to certain applications.Furthermore, it has been found that it may be desirable to form thistype of slanted structures in different types of materials (e.g.,silicon nitride, organic materials, or inorganic metal oxides, etc.).However, it may often be challenging to etch high symmetrical slantedstructures (e.g., a ridge with substantially equal leading edge andtrailing edge), deep slanted structures, or slanted structures withlarge slant angles in these materials.

According to certain embodiments, slanted gratings may be used in someoptical devices, such as waveguide displays in artificial realitysystems, to create high refractive index variations and high diffractionefficiencies. The slanted structures, such as deep or parallel slantedstructures, may not be reliably fabricated on certain materials usingcurrent known etching processes, which may generally be optimized toetch features that are perpendicular to the surface being etched, suchas the ion beam etching (IBE), reactive ion beam etching (RIBE), orchemically assisted ion beam etching (CAIBE) process. According tocertain embodiments, an ion implementation technique and a wet etchingtechnique may be used in combination to reliably etch the slantedstructures. The ion implantation process parameters, including, forexample, the ions, the ion flux, the ion energy, the implantation angle,and the implantations time, can be more precisely controlled to achievethe desired etching selectivity, desired etch rate, and desireddimensions of the slanted structures. In some embodiments, the ionimplantation technique may also be used independently to make slantedBragg-like gratings by modifying the refractive index of the implantedregions. In some embodiments, concurrent or sequential ionbombardment-based material modification strategy can be used inconjunction with a reactive gas through appropriate choice of feed gasmixture, ion source, and extraction parameters, to make slantedBragg-like gratings as defined by a hard mask.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof.

FIG. 1 is a simplified diagram of an example near-eye display 100according to certain embodiments. Near-eye display 100 may present mediato a user. Examples of media presented by near-eye display 100 mayinclude one or more images, video, and/or audio. In some embodiments,audio may be presented via an external device (e.g., speakers and/orheadphones) that receives audio information from near-eye display 100, aconsole, or both, and presents audio data based on the audioinformation. Near-eye display 100 is generally configured to operate asan artificial reality display. In some embodiments, near-eye display 100may operate as an augmented reality (AR) display or a mixed reality (MR)display.

Near-eye display 100 may include a frame 105 and a display 110. Frame105 may be coupled to one or more optical elements. Display 110 may beconfigured for the user to see content presented by near-eye display100. In some embodiments, display 110 may include a waveguide displayassembly for directing light from one or more images to an eye of theuser.

FIG. 2 is a cross-sectional view 200 of near-eye display 100 illustratedin FIG. 1. Display 110 may include may include at least one waveguidedisplay assembly 210. An exit pupil 230 may be located at a locationwhere a user's eye 220 is positioned when the user wears near-eyedisplay 100. For purposes of illustration, FIG. 2 shows cross-sectionsectional view 200 associated with user's eye 220 and a single waveguidedisplay assembly 210, but, in some embodiments, a second waveguidedisplay may be used for the second eye of the user.

Waveguide display assembly 210 may be configured to direct image light(i.e., display light) to an eyebox located at exit pupil 230 and touser's eye 220. Waveguide display assembly 210 may include one or morematerials (e.g., plastic, glass, etc.) with one or more refractiveindices. In some embodiments, near-eye display 100 may include one ormore optical elements between waveguide display assembly 210 and user'seye 220.

In some embodiments, waveguide display assembly 210 may include a stackof one or more waveguide displays including, but not restricted to, astacked waveguide display, a varifocal waveguide display, a multi-focal(or multi-planar) display, etc. The stacked waveguide display is apolychromatic display (e.g., a red-green-blue (RGB) display) created bystacking waveguide displays whose respective monochromatic sources areof different colors. The stacked waveguide display may also be apolychromatic display that can be projected on multiple planes (e.g.multi-planar colored display). In some configurations, the stackedwaveguide display may be a monochromatic display that can be projectedon multiple planes (e.g. multi-planar monochromatic display). Thevarifocal waveguide display is a display that can adjust a focalposition of image light emitted from the waveguide display. In alternateembodiments, waveguide display assembly 210 may include the stackedwaveguide display and the varifocal waveguide display.

FIG. 3 is an isometric view of an embodiment of a waveguide display 300.In some embodiments, waveguide display 300 may be a component (e.g.,waveguide display assembly 210) of near-eye display 100. In someembodiments, waveguide display 300 may be part of some other near-eyedisplays or other systems that may direct image light to a particularlocation.

Waveguide display 300 may include a source assembly 310, an outputwaveguide 320, and a controller 330. For purposes of illustration, FIG.3 shows waveguide display 300 associated with a user's eye 390, but insome embodiments, another waveguide display separate, or partiallyseparate, from waveguide display 300 may provide image light to anothereye of the user.

Source assembly 310 may generate image light 355 for display to theuser. Source assembly 310 may generate and output image light 355 to acoupling element 350 located on a first side 370-1 of output waveguide320. In some embodiments, coupling element 350 may couple image light355 from source assembly 310 into output waveguide 320. Coupling element350 may include, for example, a diffraction grating, a holographicgrating, one or more cascaded reflectors, one or more prismatic surfaceelements, and/or an array of holographic reflectors. Output waveguide320 may be an optical waveguide that can output expanded image light 340to user's eye 390. Output waveguide 320 may receive image light 355 atone or more coupling elements 350 located on first side 370-1 and guidereceived image light 355 to a directing element 360.

Directing element 360 may redirect received input image light 355 todecoupling element 365 such that received input image light 355 may becoupled out of output waveguide 320 via decoupling element 365.Directing element 360 may be part of, or affixed to, first side 370-1 ofoutput waveguide 320. Decoupling element 365 may be part of, or affixedto, a second side 370-2 of output waveguide 320, such that directingelement 360 is opposed to decoupling element 365. Directing element 360and/or decoupling element 365 may include, for example, a diffractiongrating, a holographic grating, a surface-relief grating, one or morecascaded reflectors, one or more prismatic surface elements, and/or anarray of holographic reflectors.

Second side 370-2 of output waveguide 320 may represent a plane along anx-dimension and a y-dimension. Output waveguide 320 may include one ormore materials that can facilitate total internal reflection of imagelight 355. Output waveguide 320 may include, for example, silicon,plastic, glass, and/or polymers. Output waveguide 320 may have arelatively small form factor. For example, output waveguide 320 may beapproximately 50 mm wide along the x-dimension, about 30 mm long alongthe y-dimension, and about 0.5 to 1 mm thick along a z-dimension.

Controller 330 may control scanning operations of source assembly 310.Controller 330 may determine scanning instructions for source assembly310. In some embodiments, output waveguide 320 may output expanded imagelight 340 to user's eye 390 with a large field of view (FOV). Forexample, expanded image light 340 provided to user's eye 390 may have adiagonal FOV (in x and y) of about 60 degrees or greater and/or about150 degrees or less. Output waveguide 320 may be configured to providean eyebox with a length of about 20 mm or greater and/or equal to orless than about 50 mm, and/or a width of about 10 mm or greater and/orequal to or less than about 50 mm.

FIG. 4 is a cross-sectional view 400 of waveguide display 300. Waveguidedisplay 300 may be mono or poly chromatic. Waveguide display 300 mayinclude source assembly 310 and output waveguide 320. Source assembly310 may generate image light 355 (i.e., display light) in accordancewith scanning instructions from controller 330. Source assembly 310 mayinclude a source 410 and an optics system 415. Source 410 may include alight source that generates coherent or partially coherent light. Forexample, source 410 may include a laser diode, a vertical cavity surfaceemitting laser, a light emitting diode, or a 1-D or 2-D array of lasersdiodes, VCSELs, or LEDs (e.g., a μLED array).

Optics system 415 may include one or more optical components that cancondition the light from source 410. Conditioning light from source 410may include, for example, expanding, collimating, and/or adjustingorientation in accordance with instructions from controller 330. The oneor more optical components may include one or more lenses, liquidlenses, mirrors, apertures, and/or gratings. Light emitted from opticssystem 415 (and also source assembly 310) may be referred to as imagelight 355 or display light.

Output waveguide 320 may receive image light 355 from source assembly310. Coupling element 350 may couple image light 355 from sourceassembly 310 into output waveguide 320. In embodiments where couplingelement 350 includes a diffraction grating, the diffraction grating maybe configured such that total internal reflection may occur withinoutput waveguide 320, and thus image light 355 coupled into outputwaveguide 320 may propagate internally within output waveguide 320(e.g., by total internal reflection) toward decoupling element 365.

Directing element 360 may redirect image light 355 toward decouplingelement 365 for coupling at least a portion of the image light out ofoutput waveguide 320. In embodiments where directing element 360 is adiffraction grating, the diffraction grating may be configured to causeincident image light 355 to exit output waveguide 320 at angle(s) ofinclination relative to a surface of decoupling element 365. In someembodiments, directing element 360 and/or the decoupling element 365 maybe structurally similar.

Expanded image light 340 exiting output waveguide 320 may be expandedalong one or more dimensions (e.g., elongated along the x-dimension). Insome embodiments, waveguide display 300 may include a plurality ofsource assemblies 310 and a plurality of output waveguides 320. Each ofsource assemblies 310 may emit a monochromatic image light correspondingto a primary color (e.g., red, green, or blue). Each of outputwaveguides 320 may be stacked together to output an expanded image light340 that may be multi-colored.

FIG. 5 is a simplified block diagram of an example artificial realitysystem 500 including waveguide display assembly 210. System 500 mayinclude near-eye display 100, an imaging device 535, and an input/outputinterface 540 that are each coupled to a console 510.

As described above, near-eye display 100 may be a display that presentsmedia to a user. Examples of media presented by near-eye display 100 mayinclude one or more images, video, and/or audio. In some embodiments,audio may be presented via an external device (e.g., speakers and/orheadphones) that may receive audio information from near-eye display 100and/or console 510 and present audio data based on the audio informationto a user. In some embodiments, near-eye display 100 may act as anartificial reality eyewear glass. For example, in some embodiments,near-eye display 100 may augment views of a physical, real-worldenvironment, with computer-generated elements (e.g., images, video,sound, etc.).

Near-eye display 100 may include waveguide display assembly 210, one ormore position sensors 525, and/or an inertial measurement unit (IMU)530. Waveguide display assembly 210 may include a waveguide display,such as waveguide display 300 that includes source assembly 310, outputwaveguide 320, and controller 330 as described above.

IMU 530 may include an electronic device that can generate fastcalibration data indicating an estimated position of near-eye display100 relative to an initial position of near-eye display 100 based onmeasurement signals received from one or more position sensors 525.

Imaging device 535 may generate slow calibration data in accordance withcalibration parameters received from console 510. Imaging device 535 mayinclude one or more cameras and/or one or more video cameras.

Input/output interface 540 may be a device that allows a user to sendaction requests to console 510. An action request may be a request toperform a particular action. For example, an action request may be tostart or end an application or to perform a particular action within theapplication.

Console 510 may provide media to near-eye display 100 for presentationto the user in accordance with information received from one or more of:imaging device 535, near-eye display 100, and input/output interface540. In the example shown in FIG. 5, console 510 may include anapplication store 545, a tracking module 550, and an engine 555.

Application store 545 may store one or more applications for executionby the console 510. An application may include a group of instructionsthat, when executed by a processor, may generate content forpresentation to the user. Examples of applications may include gamingapplications, conferencing applications, video playback application, orother suitable applications.

Tracking module 550 may calibrate system 500 using one or morecalibration parameters and may adjust one or more calibration parametersto reduce error in determination of the position of near-eye display100. Tracking module 550 may track movements of near-eye display 100using slow calibration information from imaging device 535. Trackingmodule 550 may also determine positions of a reference point of near-eyedisplay 100 using position information from the fast calibrationinformation.

Engine 555 may execute applications within system 500 and receivesposition information, acceleration information, velocity information,and/or predicted future positions of near-eye display 100 from trackingmodule 550. In some embodiments, information received by engine 555 maybe used for producing a signal (e.g., display instructions) to waveguidedisplay assembly 210. The signal may determine a type of content topresent to the user.

There may be many different ways to implement the waveguide display. Forexample, in some implementations, output waveguide 320 may include aslanted surface between first side 370-1 and second side 370-2 forcoupling image light 355 into output waveguide 320. In someimplementations, the slanted surface may be coated with a reflectivecoating to reflect light towards directing element 360. In someimplementations, the angle of the slanted surface may be configured suchthat image light 355 may be reflected by the slanted surface due tototal internal reflection. In some implementations, directing element360 may not be used, and light may be guided within output waveguide 320by total internal reflection. In some implementations, decouplingelements 365 may be located near first side 370-1.

In some implementations, output waveguide 320 and decoupling element 365(and directing element 360 if used) may be transparent to light from theenvironment, and may act as an optical combiner for combining imagelight 355 and light from the physical, real-world environment in frontof near-eye display 100. As such, the user can view both artificialimages of artificial objects from source assembly 310 and real images ofreal objects in the physical, real-world environment, which may bereferred to as optical see-through.

FIG. 6 illustrates an example optical see-through augmented realitysystem 600 using a waveguide display according to certain embodiments.Augmented reality system 600 may include a projector 610 and a combiner615. Projector 610 may include a light source or image source 612 andprojector optics 614. In some embodiments, image source 612 may includea plurality of pixels that displays virtual objects, such as an LCDdisplay panel or an LED display panel. In some embodiments, image source612 may include a light source that generates coherent or partiallycoherent light. For example, image source 612 may include a laser diode,a vertical cavity surface emitting laser, and/or a light emitting diode.In some embodiments, image source 612 may include a plurality of lightsources each emitting a monochromatic image light corresponding to aprimary color (e.g., red, green, or blue). In some embodiments, imagesource 612 may include an optical pattern generator, such as a spatiallight modulator. Projector optics 614 may include one or more opticalcomponents that can condition the light from image source 612, such asexpanding, collimating, scanning, or projecting light from image source612 to combiner 615. The one or more optical components may include, forexample, one or more lenses, liquid lenses, mirrors, apertures, and/orgratings. In some embodiments, projector optics 614 may include a liquidlens (e.g., a liquid crystal lens) with a plurality of electrodes thatallows scanning of the light from image source 612.

Combiner 615 may include an input coupler 630 for coupling light fromprojector 610 into a substrate 620 of combiner 615. Input coupler 630may include a volume holographic grating, a diffractive optical elements(DOE) (e.g., a surface-relief grating), or a refractive coupler (e.g., awedge or a prism). Input coupler 630 may have a coupling efficiency ofgreater than 30%, 50%, 75%, 90% , or higher for visible light. As usedherein, visible light may refer to light with a wavelength between about380 nm to about 750 nm. Light coupled into substrate 620 may propagatewithin substrate 620 through, for example, total internal reflection(TIR). Substrate 620 may be in the form of a lens of a pair ofeyeglasses. Substrate 620 may have a flat or a curved surface, and mayinclude one or more types of dielectric materials, such as glass,quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, orceramic. In some embodiments, substrate 620 may include a semiconductorwafer, a SiO₂ layer, a Si₃N₄ material layer, a titanium oxide layer, analumina layer, a SiC layer, a SiOxNy layer, an amorphous silicon layer,a spin on carbon (SOC) layer, an amorphous carbon layer (ACL), a diamondlike carbon (DLC) layer, a TiOx layer, an AlOx layer, a TaOx layer, aHFOx layer, etc. A thickness of the substrate may range from, forexample, less than about 1 mm to about 10 mm or more. Substrate 620 maybe transparent to visible light. A material may be “transparent” to alight beam if the light beam can pass through the material with a hightransmission rate, such as larger than 50%, 60%, 75%, 80%, 90%, 95%, orhigher, where a small portion of the light beam (e.g., less than 50%,40%, 25%, 20%, 10%, 5%, or less) may be scattered, reflected, orabsorbed by the material. For example, in some embodiments, thetransparent substrate may have a transmittance of 80% or higher. Thetransmission rate (i.e., transmissivity) may be represented by either aphotopically weighted or an unweighted average transmission rate over arange of wavelengths, or the lowest transmission rate over a range ofwavelengths, such as the visible wavelength range.

Substrate 620 may include or may be coupled to a plurality of outputcouplers 640 configured to extract at least a portion of the lightguided by and propagating within substrate 620 from substrate 620, anddirect extracted light 660 to an eye 690 of the user of augmentedreality system 600. As input coupler 630, output couplers 640 mayinclude grating couplers (e.g., volume holographic gratings orsurface-relief gratings), other DOEs, prisms, etc. Output couplers 640may have different coupling (e.g., diffraction) efficiencies atdifferent locations. Substrate 620 may also allow light 650 fromenvironment in front of combiner 615 to pass through with little or noloss. Output couplers 640 may also allow light 650 to pass through withlittle loss. For example, in some implementations, output couplers 640may have a low diffraction efficiency for light 650 such that light 650may be refracted or otherwise pass through output couplers 640 withlittle loss. In some implementations, output couplers 640 may have ahigh diffraction efficiency for light 650 and may diffract light 650 tocertain desired directions (i.e., diffraction angles) with little loss.As a result, the user may be able to view combined images of theenvironment in front of combiner 615 and virtual objects projected byprojector 610.

FIG. 7 illustrates propagations of incident display light 740 andexternal light 730 in an example waveguide display 700 including awaveguide 710 and a grating coupler 720. Waveguide 710 may be a flat orcurved transparent substrate with a refractive index n₂ greater than thefree space refractive index n₁ (i.e., 1.0). Grating coupler 720 mayinclude, for example, a Bragg grating or a surface-relief grating.

Incident display light 740 may be coupled into waveguide 710 by, forexample, input coupler 630 of FIG. 6 or other couplers (e.g., a prism orslanted surface) described above. Incident display light 740 maypropagate within waveguide 710 through, for example, total internalreflection. When incident display light 740 reaches grating coupler 720,incident display light 740 may be diffracted by grating coupler 720into, for example, a 0^(th) order diffraction (i.e., reflection) light742 and a −1st order diffraction light 744. The 0^(th) order diffractionmay continue to propagate within waveguide 710, and may be reflected bythe bottom surface of waveguide 710 towards grating coupler 720 at adifferent location. The −1st order diffraction light 744 may be coupled(e.g., refracted) out of waveguide 710 towards the user's eye, because atotal internal reflection condition may not be met at the bottom surfaceof waveguide 710 due to the diffraction angle of the −1^(st) orderdiffraction light 744.

External light 730 may also be diffracted by grating coupler 720 into,for example, a 0^(th) order diffraction light 732 or a −1st orderdiffraction light 734. The 0^(th) order diffraction light 732 and/or the−1st order diffraction light 734 may be refracted out of waveguide 710towards the user's eye. Thus, grating coupler 720 may act as an inputcoupler for coupling external light 730 into waveguide 710, and may alsoact as an output coupler for coupling incident display light 740 out ofwaveguide 710. As such, grating coupler 720 may act as a combiner forcombining external light 730 and incident display light 740 and send thecombined light to the user's eye.

In order to diffract light at a desired direction towards the user's eyeand to achieve a desired diffraction efficiency for certain diffractionorders, grating coupler 720 may include a blazed or slanted grating,such as a slanted Bragg grating or surface-relief grating, where thegrating ridges and grooves may be tilted relative to the surface normalof grating coupler 720 or waveguide 710. In some embodiments, tooptimize the user experience, some parameters of grating coupler 720 mayvary along the direction of light propagation within waveguide 710 suchthat the diffraction efficiency of grating coupler 720 may vary (e.g.,increase) along the same direction to achieve a substantially uniformintensity across the display.

FIG. 8 illustrates an example slanted grating 820 in an examplewaveguide display 800 according to certain embodiments. Waveguidedisplay 800 may include slanted grating 820 on a waveguide 810, such assubstrate 620. Slanted grating 820 may act as a grating coupler forcouple light into or out of waveguide 810. In some embodiments, slantedgrating 820 may include a periodic structure with a period p. Forexample, slanted grating 820 may include a plurality of ridges 822 andgrooves 824 between ridges 822. Each period of slanted grating 820 mayinclude a ridge 822 and a groove 824, which may be an air gap or aregion filled with a material with a refractive index n_(g2). The ratiobetween the width of a ridge 822 and the grating period p may bereferred to as duty cycle. Slanted grating 820 may have a duty cycleranging, for example, from about 10% to about 90% or greater. In someembodiments, the duty cycle may vary from period to period for moreaccurate image formation at user's eye. In some embodiments, the periodp of the slanted grating may vary from one area to another on slantedgrating 820, or may vary from one period to another (i.e., chirped) onslanted grating 820.

Ridges 822 may be made of a material with a refractive index of n_(g1),such as silicon containing materials (e.g., SiO₂, Si₃N₄, SiC,SiO_(x)N_(y), or amorphous silicon), organic materials (e.g., spin oncarbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon(DLC)), or inorganic metal oxide layers (e.g., TiO_(x), AlO_(x),TaO_(x), HFO_(x), etc.). Each ridge 822 may include a leading edge 830with a slant angle α and a trailing edge 840 with a slant angle β. Insome embodiments, leading edge 830 and training edge 840 of each ridge822 may be parallel to each other. In other words, slant angle α isapproximately equal to slant angle β. In some embodiments, slant angle αmay be different from slant angle β. In some embodiments, slant angle αmay be approximately equal to slant angle β. For example, the differencebetween slant angle α and slant angle β may be less than 20%, 10%, 5%,1%, or less. In some embodiments, slant angle α and slant angle β mayrange from, for example, about 30° or less to about 70% or larger.

In some implementations, grooves 824 between the ridges 822 may beover-coated or filled with a material having a refractive index n_(g2)higher or lower than the refractive index of the material of ridges 822.For example, in some embodiments, a high refractive index material, suchas Hafnia, Titania, Tungsten oxide, Zirconium oxide, Gallium sulfide,Gallium nitride, Gallium phosphide, silicon, and a high refractive indexpolymer, may be used to fill grooves 824. In some embodiments, a lowrefractive index material, such as silicon oxide, magnesium fluoride,porous silica, or fluorinated low index monomer (or polymer), may beused to fill grooves 824. As a result, the difference between therefractive index of the ridges and the refractive index of the groovesmay be greater than 0.1, 0.2, 0.3, 0.5, 1.0, or higher.

The slanted grating may be fabricated using many differentnanofabrication techniques. The nanofabrication techniques generallyinclude a patterning process and a post-patterning (e.g., over-coating)process. The patterning process may be used to form slanted ridges ofthe slanted grating. There may be many different nanofabricationtechniques for forming the slanted ridges. For example, in someimplementations, the slanted grating may be fabricated using lithographytechniques including slanted etching. In some implementations, theslanted grating may be fabricated using nanoimprint lithography (NIL)molding techniques. The post-patterning process may be used to over-coatthe slanted ridges and/or to fill the gaps between the slanted ridgeswith a material having a different refractive index than the slantedridges. The post-patterning process may be independent from thepatterning process. Thus, a same post-patterning process may be used onslanted gratings fabricated using any pattering technique.

Techniques and processes for fabricating the slanted grating describedbelow are for illustration purposes only and are not intended to belimiting. A person skilled in the art would understand that variousmodifications may be made to the techniques described below. Forexample, in some implementations, some operations described below may beomitted. In some implementations, additional operations may be performedto fabricate the slanted grating. Techniques disclosed herein may alsobe used to fabricate other slanted structures on various materials.

FIGS. 9A-9C illustrate an example simplified process for fabricating aslanted surface-relief grating by slanted etching according to certainembodiments. FIG. 9A shows a structure 900 after a lithography process,such as a photolithography process. In some embodiments, structure 900may also be transferred from an intermediate layer using a lithographyprocess. Structure 900 may include a substrate 910 that may be used asthe waveguide of a waveguide display described above, such as a glass orquartz substrate. Structure 900 may also include a layer of gratingmaterial 920, such as silicon containing materials (e.g., SiO₂, Si₃N₄,SiC, SiO_(x)N_(y), or amorphous silicon), organic materials (e.g., spinon carbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon(DLC)), or inorganic metal oxide layers (e.g., TiO_(x), AlO_(x),TaO_(x), HfO_(x), etc.). Substrate 910 may have a refractive indexn_(wg), and the layer of grating material 920 may have a refractiveindex n_(g1). In some embodiments, layer of grating material 920 may bea part of substrate 910. A mask layer 930 with a desired pattern may beformed on the layer of grating material 920. Mask layer 930 may include,for example, a photoresist material, a metal (e.g., copper, chrome,aluminum, or molybdenum), an intermetallic compound (e.g., MoSi₂), or apolymer. Mask layer 930 may be formed by, for example, the lithographyprocess.

FIG. 9B shows a structure 940 after a slanted etching process, such as adry etching process (e.g., reactive ion etching (RIE), inductivelycoupled plasma (ICP), deep silicon etching (DSE), ion beam etching(IBE), or variations of IBE). The slanted etching process may includeone or more sub-steps. The slanted etching may be performed by, forexample, rotating structure 900 and etching the layer of gratingmaterial 920 by the etching beam based on the desired slant angle. Insome embodiments, the slanted etching may be performed by spatiallyvarying the incident angle of a narrow (e.g., point or line) etchingbeam, where the etching beam may be controlled spatially by blades thatcan tune the size and location of the projected etching beam. After theetching, a slanted grating 950 may be formed in the layer of gratingmaterial 920.

FIG. 9C shows a structure 970 after mask layer 930 is removed. Structure970 may include substrate 910, the layer of grating material 920, andslanted grating 950. Slanted grating 950 may include a plurality ofridges 952 and grooves 954. Techniques such as plasma or wet etching maybe used to strip mask layer 930 with appropriate chemistry. In someimplementations, mask layer 930 may not be removed and may be used aspart of the slanted grating.

Subsequently, in some implementations, the post-patterning (e.g.,over-coating) process may be performed to over-coat slanted grating 950with a material having a refractive index higher or lower than thematerial of ridges 952. For example, as described above, in someembodiments, a high refractive index material, such as Hafnia, Titania,Tungsten oxide, Zirconium oxide, Gallium sulfide, Gallium nitride,Gallium phosphide, silicon, and a high refractive index polymer, may beused for the over-coating. In some embodiments, a low refractive indexmaterial, such as silicon oxide, magnesium fluoride, porous silica, orfluorinated low index monomer (or polymer), may be used for theover-coating. As a result, the difference between the refractive indexof the ridges and the refractive index of the grooves may be greaterthan 0.1, 0.2, 0.3, 0.5, 1.0, or higher. In some embodiments, theover-coating may be conformal (e.g., using ALD) or directional (e.g.,using sputtering or PECVD).

In different applications, slanted structures (e.g., gratings) withvarious dimensions on various materials may be desired to control thebehavior of light as the light reflects, refracts, and/or diffracts dueto the interactions with the gratings and/or the interferences betweenlight that interacts with the gratings. For example, in someapplications, it may be desirable that the leading edge and the trailingedge of the ridges of the gratings are substantially parallel. In someapplications, it may be desirable that the leading edge and the trailingedge of the ridges of the gratings have different slant angles. In someapplications, it may be desirable that the grating has a depth greaterthan, for example, a few hundred nanometers, such as a few microns. Insome applications, it may be desirable that the ridges of the gratinghave a slant angle greater than, for example, 30°, 45°, 50°, or 70°.

FIG. 10 illustrates an example slanted grating 1000 on a substrate 1010.Grating 1000 may include a plurality of ridges 1020. The distancebetween the leading or trailing edges of adjacent ridges 1020 may be p,which may be a constant or varying value across grating 1000. Each ridge1020 may have a height H, which may be a constant or varying valueacross grating 1000. Each ridge 1020 may have a regular or irregularcross-sectional shape, such as a quadrilateral. The quadrilateral mayhave a first (leading) edge 1030, a second (trailing) edge 1040, and atop edge 1050. The bottom of the quadrilateral may have a length A,which may be a constant or varying value across grating 1000. In someembodiments, first edge 1030 and second edge 1040 may be substantiallyparallel to each other. In some embodiments, top edge 1050 may beparallel to a bottom surface 1012 of substrate 1010. The region 1014between two ridges 1020 may or may not have a flat surface. The internalangles of the quadrilateral formed by the edges may include a firstangle α 1060, a second angle β 1070, and a third angle γ 1080. In someembodiments, the sum of first angle α 1060 and second angle β 1070 maybe close to 180°. In some embodiments, the sum of first angle α 1060 andthird angle γ 1080 may be close to 180°.

For many materials (e.g., silicon nitride, organic materials, orinorganic metal oxides) and/or certain desired slanted structures (e.g.,grating ridges with substantially equal leading edge and trailing edge,slanted gratings with large slant angle, or deep slanted surface-reliefgrating) many known techniques, such as the IBE process, RIBE process,and CAIBE process, may not be used to reliably fabricate the slantedstructures. According to certain embodiments, slanted ion implantation(e.g., H⁺ ion implantation), chemical etch (e.g., diluted HF etch),and/or dry etch (e.g. reactive gas such as SF6) processes may be used tomore accurately fabricate slanted structures with desired dimensions onvarious materials, including materials that may have a high refractiveindex.

Ion implantation is a low-temperature process for introducing ions ofone or more elements into a target material. In ion implantation, dopantatoms may be volatilized, ionized, accelerated, separated by themass-to-charge ratios, and directed at the target material, such as asilicon substrate. The dopant atoms may enter the target material,collide with the host atoms, lose energy, and come to rest at a certaindepth within the target material. The average penetration depth may bedetermined by the dopant, the substrate material, and the accelerationenergy. Ion implantation energies may range, for example, from aboutseveral hundred to about several million electron volts, resulting inion distributions with average depths of, for example, from about <10 nmto about >10 μm. Each ion may include a single atom or molecule, and thetotal number (dose) of ions implanted in the target is the integrationof the ion current over time. The dose and depth profile of ionimplantation can be precisely controlled. Ion implantation may beperformed in low temperature, and thus may use photoresist as mask.Other materials may also be used for the mask, such as oxide, poly-Si,metal, etc.

Ion implantation may change the physical, chemical, and/or electricalproperties of the target material. For example, the ions penetrated intothe target material can alter the elemental composition and/orelectrical conductivity of the target material when the ions differ incomposition from the target material. Ion implantation may causechemical and/or physical changes in the target material when ions with ahigh energy or speed impinge on the target material. For example, thecrystal structure of the target material may be changed or damaged bythe energetic collision.

The ion implantation equipment generally includes an ion source forgenerating ions of the desired element, an accelerator forelectrostatically accelerating the ions to a high speed (and thus a highenergy), and a target chamber where the ions may impinge on a targetmounted on a supporting structure. The supporting structure may movelinearly, rotationally, or both, such that the implantation angle, area,dose, and time may be changed by controlling the movement of thesupporting structure that holds the target.

FIG. 11A illustrates an example substrate 1110 on which slantedstructures may be formed using a mask 1120 according to certainembodiments. Substrate 1110 may include one or more types of dielectricmaterials, such as glass, quartz, plastic, polymer, poly(methylmethacrylate) (PMMA), crystal, or ceramic. In some embodiments, thecomposition of the dielectric materials (e.g., layer stack-up) insubstrate 1110 may be optimized to enable sufficient chemical and/orphysical changes in substrate 1110. In some embodiments, substrate 1110may include a semiconductor material, such as Si. In some embodiments,substrate 1110 may include a layer of material formed on a substrate,such as a Si₃N₄ or SiO₂ layer formed on a Si or other substrate. In someembodiments, substrate 1110 may include a silicon containing material(e.g., SiO₂, Si₃N₄, SiC, SiO_(x)N_(y), or amorphous silicon), an organicmaterial (e.g., spin on carbon (SOC) or amorphous carbon layer (ACL) ordiamond like carbon (DLC)), or an inorganic metal oxide layer (e.g.,TiO_(x), AlO_(x), TaO_(x), HfO_(x), etc.). Mask 1120 may include, forexample, a photoresist material, a metal (e.g., copper, chrome,aluminum, or molybdenum), an intermetallic compound (e.g., MoSi₂),poly-silicon, or a polymer. The material used for mask 1120 and thethickness of mask 1120 may be selected based on the ions to beimplanted. Mask 1120 may be thick enough such that ions may notpenetrate through the mask and reach the substrate under the mask. Ingeneral, a mask with a lower thickness is desired in order to, forexample, reduce scattering by the mask layer or not to block the ionsfrom reaching the area to be implanted. A thinner mask may be used forlighter ions, such as H⁻ ions. Mask 1120 may include a patterncorresponding to the desired cross-sectional shape of the slantedstructure, and may be formed by, for example, a lithography process.

FIG. 11B illustrates an example slanted ion implantation processaccording to certain embodiments. As shown in FIG. 11B, an ion beam 1140may impinge on substrate 1110 at a certain angle. In some embodiments,this may be achieved by rotating the substrate supporting structure to adesired angle. Mask 1120 on substrate 1110 may block a portion of theions in ion beam 1140 such that the portion of the ions would not reachsubstrate 1110. In areas that are not blocked or are only partiallyblocked by mask 1120, the ions may enter substrate 1110, collide withthe atoms in the substrate, lose energy, and finally rest at a certaindepth within substrate 1110. After the ion implantation, a plurality ofimplanted regions 1130 may be formed. The depth of implanted regions1130 may depend on the penetration depth, which may be determined by theion element, the substrate material, and the energy of the ions. Thetotal amount of ions implanted in each implanted region 1130 may dependon the ion current (flux) and the implantation time.

As described above, ion implantation may change the physical, chemical,or electrical properties of the target material. For example, a Si₃N₄material layer may not be easily etched using, for example, dilutedhydrofluoric acid (dHF), where the etch rate may be less than about 20 Åper minute at room temperature. When hydrogen ions are implanted into aSi₃N₄ material layer, the Si₃N₄ material layer may be modified accordingto:

Si₃N₄+H⁺→SiH_(x)N_(y),

where SiH_(x)N_(y) may be relatively easily etched by dHF compared withSi₃N₄. Thus, hydrogen ion implantation may change the etch rate of theSi₃N₄ material layer. The implanted regions may have a much higher etchrate using dHF than the regions without hydrogen ion implantation.Therefore, anisotropic etching of the Si₃N₄ material layer may beachieved after selective ion implantation. In some embodiments, O₂ maybe added to a Si₃N₄ film to form a Si_(x)O_(y)N_(z) material.

FIG. 11C illustrates an example slanted surface-relief structure 1150formed on substrate 1110 after one or more ion implantation and wetetching processes according to certain embodiments. As shown in FIG.11C, implanted regions 1130 shown in FIG. 11B may be etched away to formslanted grooves within substrate 1110. In some embodiments, annealingmay be performed after the ion implantation to promote the reaction, andhence the index modification and/or etch rate adjustment.

In some embodiments, the above described ion implantation process andwet etching process (e.g., using dHF or other etching solutions) may beperformed repeatedly to form deep slanted structures in the substratelayer (e.g., Si₃N₄ material layer). The depth of the slanted structuresmay depend on the penetration depth of each ion implantation process. Inthis way, slanted structures with a high aspect ratio may be fabricatedon a substrate. In some embodiments, the deep slanted structures can beachieved through simultaneous or sequential ion bombardment-basedmodification and modified layer removal with appropriate selection offeed gas mixture, ion source, and extraction parameters. The depth ofthe structures can be controlled by the etch time.

After slanted surface-relief structure 1150 is formed in substrate 1110,mask 1120 may be removed. In some embodiments, as described above, anovercoat layer may be formed on slanted surface-relief structure 1150 tofill the slanted grooves with a material having a refractive indexdifferent from the refractive index of substrate 1110.

In some embodiments, the ion implantation process described above withrespect to FIG. 11B may be used to change the optical property of thetarget material, such as the refractive index of the target material.For example, a Si₃N₄ target layer may have a refractive index between1.8 and 2.1 (e.g., 1.98). Ion implantation in the Si₃N₄ target layer(e.g., using oxygen ions) may change the implanted regions of the Si₃N₄target layer into a second material (e.g., a silicon dioxide likematerial). The second material may have a refractive index differentfrom the target material. In some embodiments, the refractive index ofthe second material may be lower than the refractive index of the targetmaterial. For example, the refractive index of the second material(e.g., SiO₂ like material) may be between 1.3 and 1.6, such as 1.46.Thus, a relatively high refractive index variation may be created withinthe target to form a Bragg-like grating. In some embodiments, dependingon the ions used for the implantation, the refractive index of thesecond material may be higher than the refractive index of the targetmaterial.

In some applications, it may be desirable that the slanted structuresare not uniform across the substrate. For example, some gratingstructures may work for light in a certain wavelength range and/orwithin a certain field of view. For light of different wavelength and/orwithin a different field of view, different grating structures may beneeded. Thus, in some implementations, the slanted structures mayinclude different structures at different areas in order to moreeffectively interact with (e.g., diffract) light in a wide wavelengthrange and within a large field of view. For example, the slantedstructures may have different periods, different slant angles, differentdepths, different refractive index variations, or any combinationthereof, in different areas on the substrate. Techniques described abovemay be used to make such slanted structures as described in detailbelow.

FIG. 12 illustrates an example process for fabricating a slantedstructure 1230 with a variable refractive index on a substrate 1210according to certain embodiments. As described above, the refractiveindex of the substrate may be changed by ion implantation. The amount ofrefractive index change may depend on the ions used and the dose of theion implantation. By selectively applying an ion implantation (e.g.,changing the dose of the ions) at different regions of substrate 1210(e.g., a Si₃N₄ substrate) using an ion beam 1240 and a mask 1220 (and/ora shutter), slanted structure 1230 having the variable refractive indexmay be formed on substrate 1210. The dose of the ions implanted into aregion of substrate 1210 may be controlled by controlling the ioncurrent and/or the implantation time. In some implementations, theimplantation time may be controlled by a shutter or may be controlled bycontrolling the moving speed of the substrate supporting structure thatholds the substrate. For example, as shown in FIG. 12, the dose of theions (e.g., oxygen ions) implanted into region 1232 may be higher thanthe dose of the ions implanted into region 1234, and thus region 1232may have a lower refractive index than region 1234. Similarly, the doseof the ions implanted into region 1234 may be higher than the dose ofthe ions implanted into region 1236, and thus region 1234 may have alower refractive index than region 1236. Thus, slanted structure 1230may have different refractive indexes and thus different diffractiveperformances (e.g., diffractive efficiencies) at regions 1232, 1234, and1236.

FIG. 13 illustrates an example process for fabricating a slantedstructure 1330 with a variable depth on a substrate 1310 according tocertain embodiments. As described above, the depth of slanted structure1330 may depend on the ion penetration depth, which may in turn dependon the ion element, the substrate material, and the energy of the ions.Thus, by varying the energy of the ions in an ion beam 1340 applied todifferent regions of substrate 1310 using a mask 1320, slanted structure1330 having different depths at different regions may be formed insubstrate 1310. In some implementations, the ion energy may be changedby changing the acceleration voltage of the accelerator in the ionimplantation equipment.

FIG. 14 illustrates an example process for fabricating a slantedstructure 1430 with a variable slant angle on a substrate 1410 accordingto certain embodiments. The slant angle of slanted structure 1430 may bechanged by changing the angle of an ion beam 1440 with respect to thesurface normal of substrate 1410. In some implementations, the angle ofion beam 1440 with respect to the surface normal of substrate 1410 maybe changed by changing a rotation angle of a substrate supportingstructure in the ion implantation equipment.

The techniques described above with respect to FIGS. 12-14 may be usedindividually or in any combination to fabricate slanted structures witha varying slant angle, depth, and/or refractive index in a substrate.For example, in some embodiments, different regions of the substrate maybe implanted at different angles with ions having different energies toform implanted regions with different slant angles and depths. Due tothe etch rate difference between the substrate and implanted regions, aslanted surface-relief structure with a varying slant angle and depthmay be formed in the substrate. When an overcoat layer is formed on theslanted surface-relief structures, the over-coated material filled inthe gaps in the surface-relief structure may have a varying slant angleand depth across the substrate. In some implementations, the abovedescribed techniques may also be used to modify the refractive index ofat least some regions of the overcoat layer. In some implementations,the above described techniques may also be applied to the overcoat layerto form a structure with a varying slant angle, depth, or refractiveindex in the overcoat layer.

FIG. 15 is a simplified flow chart 1500 illustrating an example methodof fabricating a slanted structure according to certain embodiments. Theoperations described in flow chart 1500 are for illustration purposesonly and are not intended to be limiting. In various implementations,modifications may be made to flow chart 1500 to add additionaloperations or to omit some operations. The operations described in flowchart 1500 may be performed using, for example, ion implantationequipment and/or wet etching equipment.

At block 1510, a mask layer may be formed on a material layer. Thematerial layer may include one or more types of dielectric materials,such as glass, quartz, plastic, polymer, PMMA, crystal, or ceramic. Insome embodiments, the material layer may include a semiconductormaterial, such as Si. In some embodiments, the material layer mayinclude a silicon containing material (e.g., SiO₂, Si₃N₄, SiC,SiO_(x)N_(y), or amorphous silicon), an organic material (e.g., spin oncarbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon(DLC)), or an inorganic metal oxide layer (e.g., TiO_(x), AlO_(x),TaO_(x), HfO_(x), etc.). The mask layer may include, for example, aphotoresist material, a metal (e.g., copper, chrome, aluminum, ormolybdenum), an intermetallic compound (e.g., MoSi₂), poly-silicon, or apolymer. The material used for the mask layer and the thickness of themask layer may be selected based on the ions to be implanted. Forexample, a thinner mask layer may be used for lighter ions, such as H⁺ions. The mask layer may be thick enough such that ions may notpenetrate through the mask and reach the material layer under the mask.The mask layer may include a pattern corresponding to the desiredcross-sectional shape of the slanted structure, and may be formed by,for example, a lithography process.

At block 1520, the material layer may be implanted with an ion beam at aslant angle using the mask layer. The slant angle may be measured withrespect to a surface normal of the material layer. In some embodiments,the slant angle may be greater than 30°, 45°, 50°, 70°, or larger. Insome implementations, the slant angle may be controlled by rotating thematerial layer with respect to the ion beam using, for example, arotatable supporting structure that can hold the material layer. Themask layer on the material layer may block a portion of the ions in theion beam such that the portion of the ions would not reach the materiallayer. In areas that are not blocked or only partially blocked by themask layer, the ions may enter the material layer, collide with theatoms in the material layer, and rest at some depth within the materiallayer. After the ion implantation, a plurality of implanted regions maybe formed in the material layer. The depth of the implanted regions maydepend on the penetration depth, which may depend on the ion element,the substrate material, and the energy of the ions. The total amount ofions implanted in each implanted region may depend on the ion current(flux) and the implantation time. In some embodiments, the ions in theion beam may include hydrogen ions or oxygen ions. In some embodiments,during the implanting, the material layer may be rotated to vary theslant angle for the plurality of implanted regions across the slantedstructure. In some embodiments, during the implanting, the ion energy ofthe ions in the ion beam may be adjusted to change the depth of theplurality of implanted regions across the slanted structure. In someembodiments, during the implanting, different amounts of ions may beimplanted into different regions of the plurality of implanted regionsby using different ion currents for the ion beam, different implantationtime, or both. Implanting ions into the material layer may change therefractive index, etch rate, or both of the implanted regions. Forexample, implanting oxygen ions into a Si₃N₄ material layer may form aSiO₂ like material in the implanted regions, which may reduce therefractive index of the implanted region. Thus, a slanted Bragg-likegrating may be formed after the implantation due to the refractive indexchanges caused by the ion implantation.

Optionally, at block 1530, the material layer may be wet-etched or dryetched to remove materials in the implanted regions to form a slantedsurface-relief structure. As described above, implanting ions into thematerial layer may change the etch rate of the implanted regions. Forexample, implanting hydrogen ions into a Si₃N₄ material layer maysignificantly increase the etch rate of the implanted regions usingdiluted HF relative to the etch rate of the regions of the materiallayer that are not implanted with hydrogen ions. Thus, wet etching theselectively implanted material layer using diluted HF can be highlyanisotropic, and may remove materials in the implanted regions whilekeeping the materials in the regions that are nor ion-implanted. Thus, aslanted surface-relief structure may be formed. The slant angle of theslanted surface-relief structure may correspond to the slant angle ofthe ion implantation, and the depth of the slanted surface-reliefstructure may depend on the ion energy of the ions in the ion beam asdescribed above.

Optionally, at block 1540, if the desired depth of the slantedsurface-relief structure is reached, the process may proceed tooperations at block 1550. If the desired depth of the slantedsurface-relief structure has not been reached, the process may proceedto operations at block 1520. For example, in some embodiments, it may bedesirable that the depth of the slanted surface-relief structure isgreater than 200 nm, 500 nm, 1 um, or 2 um. Thus, a single ionimplantation process and a single wet etching process may not be able toachieve the desired depth due to, for example, the limitation of theachievable ion energy of the ions for the implantation and/or thelimitation of the thickness of the mask layer that can block ions with ahigh ion energy. Therefore, in some implementations, multiple cycles ofthe operations at blocks 1520 and 1530 may be performed to etch aportion of the material layer in each cycle, such that the desired depthmay be achieved after the multiple cycles of ion implantation and wetetching.

Optionally, at block 1550, the mask layer may be removed. As describedabove, techniques such as plasma or wet etching may be used to strip themask layer with appropriate chemistry.

Optionally, at block 1560, the material layer with the slanted structuremay be coated with a material having a refractive index different fromthe refractive index of the material layer. For example, in someembodiments, a high refractive index material, such as Hafnia, Titania,Tungsten oxide, Zirconium oxide, Gallium sulfide, Gallium nitride,Gallium phosphide, silicon, or a high refractive index polymer, may beused to coat the slanted grating and/or fill the gaps in the slantedsurface-relief structure. In some embodiments, a low refractive indexmaterial, such as silicon oxide, magnesium fluoride, porous silica, orfluorinated low index monomer (or polymer), may be used to coat theslanted structure and/or fill the gaps in the slanted surface-reliefstructure. As a result, a slanted grating with a refractive indexvariation of greater than 0.1, 0.2, 0.3, 0.5, 1.0, or higher may beformed.

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, for example, a virtualreality (VR), an augmented reality (AR), a mixed reality (MR), a hybridreality, or some combination and/or derivatives thereof. Artificialreality content may include completely generated content or generatedcontent combined with captured (e.g., real-world) content. Theartificial reality content may include video, audio, haptic feedback, orsome combination thereof, and any of which may be presented in a singlechannel or in multiple channels (such as stereo video that produces athree-dimensional effect to the viewer). Additionally, in someembodiments, artificial reality may also be associated withapplications, products, accessories, services, or some combinationthereof, that are used to, for example, create content in an artificialreality and/or are otherwise used in (e.g., perform activities in) anartificial reality. The artificial reality system that provides theartificial reality content may be implemented on various platforms,including a head-mounted display (HMD) connected to a host computersystem, a standalone HMD, a mobile device or computing system, or anyother hardware platform capable of providing artificial reality contentto one or more viewers.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

What is claimed is:
 1. A method of fabricating a slanted structure on amaterial layer, the method comprising: forming a mask layer on thematerial layer; and implanting ions into a plurality of regions of thematerial layer at a slant angle greater than zero using an ion beam andthe mask layer, wherein the slant angle is measured with respect to asurface normal of the material layer, wherein implanting the ions intothe plurality of regions of the material layer changes a refractiveindex or an etch rate of the plurality of regions of the material layer.2. The method of claim 1, wherein the material layer comprises one ormore of a transparent substrate, a semiconductor substrate, a SiO₂layer, a Si₃N₄ material layer, a titanium oxide layer, an alumina layer,a SiC layer, a SiO_(x)N_(y) layer, an amorphous silicon layer, a spin oncarbon (SOC) layer, an amorphous carbon layer (ACL), a diamond likecarbon (DLC) layer, a TiO_(x) layer, an AlO_(x) layer, a TaO_(x) layer,and an HFO_(x) layer.
 3. The method of claim 1, wherein the ionscomprise hydrogen ions or oxygen ions.
 4. The method of claim 1, furthercomprising: wet-etching the material layer using an etchant to removematerials in the plurality of regions of the material layer.
 5. Themethod of claim 4, wherein: the material layer comprises a Si₃N₄material layer; the ions comprise hydrogen ions; and the etchantcomprises a diluted hydrofluoric acid.
 6. The method of claim 4, furthercomprising: performing the implanting and wet-etching repeatedly until apredetermined depth of the slanted structure is reached.
 7. The methodof claim 6, wherein: the predetermined depth of the slanted structure isgreater than 100 nm.
 8. The method of claim 1, wherein implanting ionsinto the plurality of regions of the material layer at a slant anglegreater than zero comprises at least one of: rotating the material layerduring the implanting to vary the slant angle for the plurality ofregions; or changing an ion energy of the ions during the implanting tochange an implantation depth for the plurality of regions.
 9. The methodof claim 8, further comprising: wet-etching the material layer using anetchant to remove materials in the plurality of regions of the materiallayer; removing the mask layer; and forming an overcoat layer on thematerial layer.
 10. The method of claim 9, further comprising:performing ion implantation on the overcoat layer to change refractiveindexes in some regions of the overcoat layer.
 11. The method of claim10, wherein the overcoat layer includes one or more of fluorinated SiO₂,porous silicate, SiO_(x)N_(y), HFO₂, and Al₂O₃.
 12. The method of claim1, further comprising: etching the material layer using a reactive gaswhile implanting ions into the plurality of regions of the materiallayer using the ion beam.
 13. The method of claim 1, wherein implantingions into the plurality of regions of the material layer comprises:implanting different amounts of ions into different regions of theplurality of regions by using different ion currents for the ion beam,different implantation times, or both when implanting different regionsof the plurality of regions.
 14. The method of claim 1, wherein: thematerial layer comprises a Si₃N₄ material layer; and the ions compriseoxygen ions.
 15. The method of claim 1, wherein: the slant angle isgreater than 45°.
 16. An ion implantation system for fabricating aslanted optical device on a substrate, the ion implantation systemcomprising: an ion source for generating ions of a chemical element; anaccelerator for electrostatically accelerating the ions; a targetchamber comprising a supporting structure, wherein the supportingstructure is configured to hold the substrate and is rotatable withrespect to a moving direction of the ions; and a controller configuredto change a rotation angle of the supporting structure such that theions impinge on the substrate at a predetermined slant angle.
 17. Theion implantation system of claim 16, wherein the controller is furtherconfigured to control at least one of: a speed of the ions; a flux ofthe ions; an implantation time; a rotation speed of the supportingstructure; or a linear moving speed of the supporting structure.
 18. Theion implantation system of claim 16, wherein the controller is furtherconfigured to: rotate the supporting structure to different rotationangles for implanting different regions of the substrate; accelerate theions to different speeds for implanting different regions of thesubstrate; or implanting different numbers of ions into differentregions of the substrate.
 19. The ion implantation system of claim 16,wherein: the chemical element comprises hydrogen or oxygen; and thesubstrate comprises a Si₃N₄ layer.
 20. A slanted surface-relief gratingobtained by a process, the process comprising: forming a mask layer on amaterial layer; implanting ions into a plurality of regions of thematerial layer at a slant angle greater than 30° using an ion beam andthe mask layer, wherein the slant angle is measured with respect to asurface normal of the material layer; and wet-etching the material layerusing an etchant to remove materials in the plurality of regions of thematerial layer.
 21. The slanted surface-relief grating of claim 20,wherein: the material layer comprises a Si₃N₄ material layer; the ionscomprise hydrogen ions; and the etchant comprises a diluted hydrofluoricacid.
 22. The slanted surface-relief grating of claim 20, wherein theprocess further comprises: performing the implanting and wet-etchingrepeatedly until a predetermined depth of the slanted surface-reliefgrating is reached, wherein the predetermined depth is greater than 100nm.